While the main driver of explosive volcanic eruptions was thought to be the presence of water in the magma, a new study suggests that in the case of some volcanoes, it would be CO2.2 who should be implicated.
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What happens when magma heated to over 1,000°C is mixed with water? The latter would suddenly vaporize and turn into a gaseous form, causing an explosion. This phenomenon is called hydromagmatism. It is responsible for some of the most powerful explosive eruptions in history and is commonly seen in the case of volcanoes located at shallow depths below the surface of the ocean or whose craters are occupied by a lake or lie beneath a glacier.
Water, the engine of the explosive detonation?
But hydromagmatism is not just that. Water is actually a volatile element among other elements present in magma in variable proportions. If the mixing is stable at depth, the water will slowly change to gaseous form by a decrease in pressure as the magma rises. This is an elimination process. The amount of water gained by the magma in contact with the rocks will thus determine the intensity of the eruptions, which will allow the magma to reach the surface. Water has therefore long been considered one of the main drivers of explosive eruptions.
A new study published in the journal PNAS However, it has been demonstrated that it will not be the only one.
The Special Case of Explosive Basaltic Volcanoes
Researchers from Cornell University in the United States have really looked into the mechanisms behind explosive basaltic eruptions. In general, basaltic volcanoes, whose lava is very fluid, are not considered very explosive volcanoes. Unlike highly active volcanoes found in subduction zones, such as those in the Pacific Ring of Fire, basaltic volcanoes are located in intraplate domains. So they are not located at the edge of tectonic plates but somewhere above. Because of the thickness of the crust on which they rest, these volcanoes are fed by magma produced at great depths, about 20 to 30 kilometers below the surface and associated with mantle plumes (hot spots). The typical example that is often used to illustrate this type of volcano is Hawaii. However, this generalization of the Hawaiian type has obscured some of the properties of these basaltic volcanoes, particularly their ability to produce explosive eruptions.
Magma is generated at great depth and rises very quickly through the earth’s crust.
Thus Fogo Volcano appears to be an extreme case of a basaltic volcano exhibiting explosive activity. Located on the oceanic crust of the African Plate, it forms an island of the same name that is part of Cape Verde, west of Senegal in the Atlantic Ocean. To determine the cause of this volcanic behavior, scientists were interested in the composition of the volcanic rocks produced by Fogo, and in particular the presence of volatile elements. Thus he analyzed the microscopic bubbles of gas trapped in the crystal at the time of the explosion. High concentration of CO detected by this method2, This observation suggests that the magma was stored deep within the mantle and not within the crust.
increase in magma due to CO2
However, at the time of its passage the magma is filled with water and, from a strong, from its temporary storage in the earth’s crust. In the case of Fogo, the magma would have passed through the crust so rapidly that its water content would have been the engine of the eruption here. For the researchers, everything will depend on the carbon dioxide present in the magma and its emissions during ascent.
These new results completely revolutionize our view of how this type of volcano works and really have an impact on the understanding of the associated volcanic hazard.
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